The quilt patch titled
Subject: Revert "mm: vmscan: make memcg slab shrink lockless"
has been removed from the -mm tree. Its filename was
revert-mm-vmscan-make-memcg-slab-shrink-lockless.patch
This patch was dropped because it was merged into the mm-hotfixes-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
------------------------------------------------------
From: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
Subject: Revert "mm: vmscan: make memcg slab shrink lockless"
Date: Fri, 9 Jun 2023 08:15:17 +0000
This reverts commit caa05325c9126c77ebf114edce51536a0d0a9a08.
Kernel test robot reports -88.8% regression in stress-ng.ramfs.ops_per_sec
test case [1], which is caused by commit f95bdb700bc6 ("mm: vmscan: make
global slab shrink lockless"). The root cause is that SRCU has to be
careful to not frequently check for SRCU read-side critical section exits.
Therefore, even if no one is currently in the SRCU read-side critical
section, synchronize_srcu() cannot return quickly. That's why
unregister_shrinker() has become slower.
After discussion, we will try to use the refcount+RCU method [2] proposed
by Dave Chinner to continue to re-implement the lockless slab shrink. So
revert the shrinker_srcu related changes first.
[1]. https://lore.kernel.org/lkml/202305230837.db2c233f-yujie.liu@xxxxxxxxx/
[2]. https://lore.kernel.org/lkml/ZIJhou1d55d4H1s0@xxxxxxxxxxxxxxxxxxx/
Link: https://lkml.kernel.org/r/20230609081518.3039120-7-qi.zheng@xxxxxxxxx
Reported-by: kernel test robot <yujie.liu@xxxxxxxxx>
Closes: https://lore.kernel.org/oe-lkp/202305230837.db2c233f-yujie.liu@xxxxxxxxx
Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
Cc: Dave Chinner <david@xxxxxxxxxxxxx>
Cc: Kirill Tkhai <tkhai@xxxxx>
Cc: Muchun Song <muchun.song@xxxxxxxxx>
Cc: Roman Gushchin <roman.gushchin@xxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/vmscan.c | 45 +++++++++++++++++++--------------------------
1 file changed, 19 insertions(+), 26 deletions(-)
--- a/mm/vmscan.c~revert-mm-vmscan-make-memcg-slab-shrink-lockless
+++ a/mm/vmscan.c
@@ -210,21 +210,8 @@ static inline int shrinker_defer_size(in
static struct shrinker_info *shrinker_info_protected(struct mem_cgroup *memcg,
int nid)
{
- return srcu_dereference_check(memcg->nodeinfo[nid]->shrinker_info,
- &shrinker_srcu,
- lockdep_is_held(&shrinker_rwsem));
-}
-
-static struct shrinker_info *shrinker_info_srcu(struct mem_cgroup *memcg,
- int nid)
-{
- return srcu_dereference(memcg->nodeinfo[nid]->shrinker_info,
- &shrinker_srcu);
-}
-
-static void free_shrinker_info_rcu(struct rcu_head *head)
-{
- kvfree(container_of(head, struct shrinker_info, rcu));
+ return rcu_dereference_protected(memcg->nodeinfo[nid]->shrinker_info,
+ lockdep_is_held(&shrinker_rwsem));
}
static int expand_one_shrinker_info(struct mem_cgroup *memcg,
@@ -265,7 +252,7 @@ static int expand_one_shrinker_info(stru
defer_size - old_defer_size);
rcu_assign_pointer(pn->shrinker_info, new);
- call_srcu(&shrinker_srcu, &old->rcu, free_shrinker_info_rcu);
+ kvfree_rcu(old, rcu);
}
return 0;
@@ -351,16 +338,15 @@ void set_shrinker_bit(struct mem_cgroup
{
if (shrinker_id >= 0 && memcg && !mem_cgroup_is_root(memcg)) {
struct shrinker_info *info;
- int srcu_idx;
- srcu_idx = srcu_read_lock(&shrinker_srcu);
- info = shrinker_info_srcu(memcg, nid);
+ rcu_read_lock();
+ info = rcu_dereference(memcg->nodeinfo[nid]->shrinker_info);
if (!WARN_ON_ONCE(shrinker_id >= info->map_nr_max)) {
/* Pairs with smp mb in shrink_slab() */
smp_mb__before_atomic();
set_bit(shrinker_id, info->map);
}
- srcu_read_unlock(&shrinker_srcu, srcu_idx);
+ rcu_read_unlock();
}
}
@@ -374,6 +360,7 @@ static int prealloc_memcg_shrinker(struc
return -ENOSYS;
down_write(&shrinker_rwsem);
+ /* This may call shrinker, so it must use down_read_trylock() */
id = idr_alloc(&shrinker_idr, shrinker, 0, 0, GFP_KERNEL);
if (id < 0)
goto unlock;
@@ -407,7 +394,7 @@ static long xchg_nr_deferred_memcg(int n
{
struct shrinker_info *info;
- info = shrinker_info_srcu(memcg, nid);
+ info = shrinker_info_protected(memcg, nid);
return atomic_long_xchg(&info->nr_deferred[shrinker->id], 0);
}
@@ -416,7 +403,7 @@ static long add_nr_deferred_memcg(long n
{
struct shrinker_info *info;
- info = shrinker_info_srcu(memcg, nid);
+ info = shrinker_info_protected(memcg, nid);
return atomic_long_add_return(nr, &info->nr_deferred[shrinker->id]);
}
@@ -947,14 +934,15 @@ static unsigned long shrink_slab_memcg(g
{
struct shrinker_info *info;
unsigned long ret, freed = 0;
- int srcu_idx;
int i;
if (!mem_cgroup_online(memcg))
return 0;
- srcu_idx = srcu_read_lock(&shrinker_srcu);
- info = shrinker_info_srcu(memcg, nid);
+ if (!down_read_trylock(&shrinker_rwsem))
+ return 0;
+
+ info = shrinker_info_protected(memcg, nid);
if (unlikely(!info))
goto unlock;
@@ -1004,9 +992,14 @@ static unsigned long shrink_slab_memcg(g
set_shrinker_bit(memcg, nid, i);
}
freed += ret;
+
+ if (rwsem_is_contended(&shrinker_rwsem)) {
+ freed = freed ? : 1;
+ break;
+ }
}
unlock:
- srcu_read_unlock(&shrinker_srcu, srcu_idx);
+ up_read(&shrinker_rwsem);
return freed;
}
#else /* CONFIG_MEMCG */
_
Patches currently in -mm which might be from zhengqi.arch@xxxxxxxxxxxxx are
